Extensive comparison 22 kHz vocalizations in rats with human cry: 76% of common features; vocalizations may be an evolutionary vocal homolog of human crying, expressing anxiety, not depression

Emission of 22 kHz vocalizations in rats as an evolutionary equivalent of human crying: Relationship to depression. Stefan M. Brudzynski. Behavioural Brain Research, https://doi.org/10.1016/j.bbr.2019.01.033

Highlights
•    Rat 22 kHz ultrasonic vocalizations (USVs) were compared with human crying
•    Extensive comparison of 22 kHz USV with human cry showed 76% of common features
•    Rat 22 kHz USVs may be treated as an evolutionary vocal homolog of human crying
•    Rat 22 kHz USVs and human crying are both expressing anxiety and not depression

Abstract: There is no clear relationship between crying and depression based on human neuropsychiatric observations. This situation originates from lack of suitable animal models of human crying. In the present article, an attempt will be made to answer the question whether emission of rat aversive vocalizations (22 kHz calls) may be regarded as an evolutionary equivalent of adult human crying. Using this comparison, the symptom of crying in depressed human patients will be reanalyzed. Numerous features and characteristics of rat 22 kHz aversive vocalizations and human crying vocalizations are equivalent. Comparing evolutionary, biological, physiological, neurophysiological, social, pharmacological, and pathological aspects have shown vast majority of common features. It is concluded that emission of rat 22 kHz vocalizations may be treated as an evolutionary vocal homolog of human crying, although emission of 22 kHz calls is not exactly the same phenomenon because of significant differences in cognitive processes between these species. It is further concluded that rat 22 kHz vocalizations and human crying vocalizations are both expressing anxiety and not depression. Analysis of the relationship between anxiety and depression reported in clinical studies supports this conclusion regardless of the nature and extent of comorbidity between these pathological states.